たが[最後「さいご」] => Once A occurs, B happens N1
Information, Report
[最中「さいちゅう」] => In the middle of A N3
Time, Situation
[要「よう」]するに => A. In short/put simply, B N2
Adjectival, Descriptions
[必要「ひつよう」]はない => It is not necessary for A to be done N2
Needs, Requirements